A two-part idiom (歇後語); the second part is 唔打唔成器. 柴魚命 means "the life of a 柴魚". 柴魚 is a type of fish used in making soup or porridge. In order for its flavour to be released into the broth or porridge, it has to be beatened and hammered. in this way, the "life of 柴魚" is such that it is "唔打唔成器", which would mean "not aromatic if not beatened ". note that there is a pun on the character 器(sounds like 氣).